1. Field of the Invention
The invention relates to a working device for a ground-processing device having a milling drum with a milling drum tube on whose surface working tools are mounted in a projecting manner and are intended to come into contact with the material to be milled during the milling process, wherein the working device comprises a powertrain for driving the milling drum.
2. Description of the Prior Art
Ground-processing machines are known in a wide variety of embodiments. For example, DE 201 22 928 U1 (U.S. Pat. No. 7,644,994) discloses a road milling machine as a ground-processing machine. It has a powertrain. This comprises a drive engine, a shifting clutch and a gearbox (what is referred to as the “milling drum gearbox”), and also elements, in particular shafts, toothed or endless drives, which interconnect these units. Within the scope of the invention, a powertrain is to be understood in particular under the above definition. According to DE 201 22 928 U1, use is made of a milling drum which is fitted with working tools on the surface of its milling drum tube. Working tools are to be understood as meaning the constructional units of the milling drum which functionally interact with the material to be milled during the working process. For example, these are milling chisels and the holder systems supporting the milling chisels. Furthermore, working tools frequently mounted on the milling drum are guiding and ejecting tools. These have guiding and conveying functions.
When using a machine according to the invention, the work result is decisively influenced by the rotational speed of the milling drum. In this context, the optimal rotational speed is generally dependent on the application.
During fine milling of road surfaces, to restore the skid resistance, with a small milling depth, relatively high rotational speeds are required in order to produce a uniform milling pattern. Therefore, only a surface processing takes place here.
When removing all or a number of layers of the road structure, lower rotational speeds tend to be more favorable since it has been shown that, as a result, a better milling pattern with a smaller generation of fine particle fragments, and therefore reduced dust generation, can be ensured. Moreover, the wear on the milling tools is considerably reduced at low rotational speeds. Furthermore, with a reduced rotational speed of the milling drum, a reduced output power of the drive is also required and thus a lower fuel consumption is made possible. Overall, it should therefore be sought to achieve a rotational speed of the milling drum which is as low as possible in such applications.
In order to meet the various requirements, it is therefore known to be able to variably set the rotational speed of the milling drum in road milling machines.
However, if the rotational speed is selected to be too low, the kinetic energy of the milling drum is no longer sufficient to effectively process the material to be milled, there occurring an out-of-round and unsmooth running of the milling drum which is demonstrated, inter alia, by vibrations of the entire ground-processing machine right through to unstable oscillation of the machine, here possibly also resulting in damage to the machine. Furthermore, the work quality suffers as a result of the unsmooth running of the milling drum, and unevenness in the milling pattern can occur. In the extreme case, it is possible for the milling drum to “bog down” if the kinetic energy is not sufficient.
A high weight of the ground-processing machine contributes to increasing the running smoothness even at low rotational speeds. However, this is disadvantageous in many respects since as a result, on the one hand, particular requirements must be placed on transportation (large milling machines>40t→heavy transport) and, on the other hand, the use possibilities are restricted to grounds which have statically little load-bearing capacity.
It is therefore known to load milling machines for stabilization purposes. For this purpose, additional weights are fastened on the machine. Thus, it is known for example that, in a road milling machine having a total weight of about 4.5 tonnes, 1.3 tonnes can be made available by means of additional weights. In other words, the additional weights make up barely ⅓ of the machine weight. Such a machine can thus be used flexibly but must be loaded with large additional weights for optimal adaptation to the respective task.
U.S. Pat. No. 4,006,936 A discloses a ground-processing machine having a milling device. To improve the running smoothness of the milling drum, the use of a milling drum tube which has a greater wall thickness than customary milling drum tubes is recommended. This course of action proves to be disadvantageous particularly during manufacture since the milling drum tubes are rolled from a sheet-like blank. The rolled blank is then welded at its longitudinal-side abutment points. The tube thus manufactured and welded must then be turned. The large material thickness increases the manufacturing expenditure. The use of the relatively thick blank causes a considerable increase in the forming work expenditure. Owing to the large wall thickness, the milling drum tube can be manufactured only with a significant degree of out-of-roundness, with the result that increased machining effort is required during turning.
Moreover, in this design of the milling drum tube, flexible adaptation to the respective task cannot occur.